Production of thiophene-free benzene



are obtained by the dry distillation of coal.

Patented Apr. '11, 1944 rr onUcrIoN F THIOPHENE-FREE BENZENE Heber Von Lauer, Gary, 11111., and George Charles Ponchaud, Joliet, Ill.

No Drawing. Application June 18, 1942,

Serial No. 447,668

9 Claims.

For the production of many chemical products employed in the related explosives and dye industries, there are required large quantities of pure benzene, which forms the starting material for a wide variety of such products. Thus pure benzene is employed in the manufacture of synthetic phenol, in the production of nitrobenzene which may be converted readily into aniline, and in the manufacture of toluol, to mention only a few compounds obtainable from benzene as the starting material, and whose nitration products and derivatives find wide application in the fields of explosives, dye-stuffs, and pharmaceuticals.

The most important source of benzene is bituminous coal from which" it is obtained by dry distillation, it being present, therefore, in coal tar. This benzene is, in fact, the parent hydrocarbon of all of the aromatic, or carbocyclic compounds. 7

The production of pure benzene is rather involved. It will be recalled that not only benzene, but also numerous methyl benzenes, and many more highly condensed aromatic hydrocarbons, such as naphthalene, acenaphthene, fluorene, anthracene and phenanthrene, fiuoranthrene, pyrene, chrysene, and innumerable other compounds They are present in coal tar, which is produced in great quantities in the manufacture of illuminating gas and in the coke industry.

The rapid, well-known development of the chemistry of the benzene derivatives is due largely to the fact that the aromatic parent hydrocarbonsare present so largely in coal tar and coke oven light oils and are accessible in large amounts through various technical industries. While in the case of the parafiins their very-nature renders them unsuitable for the preparation of the aromatic bodies; the benzene hydrocarbons on the other hand, because of the readiness with which they enter into all kinds of reactions,constitute not only the systematic, but also the practical foundation for the unbuilding of the chemistry of the'aromatic derivatives. Coal tar; and more especially coke oven light oils, which contains these hydrocarbons is .an inexhaustible source for the preparation of benzene and numerous benzene derivatives, many of which are of highest strategic importance militarily, and also constitute the foundation of the dye industry,

while also in many instances constituting important sources of valuable pharmaceutical products.

Coal tar and coke oven light oils contain not only aromatic hydrocarbons, but also paraffins, thiophene, methylated thiophenes, phenols, pyridine bases, and other derivatives. Coke oven light oil, which is one of the greatest sources for the preparation of benzene, is usually scrubbed from coke oven gas with a straw or absorbent oil. The absorbent oil, laden with benzene homologous paraflins, thiophene, pyridine, and other compounds, is usually separated into two fractions, the lightest of which, known as primary light oil, is specifically lighter thanwater, and boils up to 160 C. It contains benzene, toluene, xylene associated with other materials such as resins, olefines, parafiins, thiophene and pyridine bases.

For recovering the benzene contained therein, the crude light oil is subjected to fractional distillation, removing the highly volatile forerunnings, which leaves a product boiling from between about C. and about C. This fraction is freed from resins, ,olefines, pyridine bases,

and other unsaturated compounds, by washing with 66 B. sulphuric acid in suitable amounts, for instance 540 pounds of the acid to 5,500 gallons of the oil. The acid is drained from the agitator and the acidified oil is neutralized with caustic soda, for instance a 20 per cent caustic soda solution, which both neutralizes the acid and removes the phenols from the oil.

The thus "sWeete-ned oil is separated from the aqueous layer and charged to a fractionating still and carefully fractionated, there being recovered motor benzene, pure benzene, toluol, and xylol of standard quality.

All grades of benzene hus normally recovered contain varying 'amounts of thiophene and, since the sulphur of .the thiophene renders explosives produced from the benzene hypersensitive, interfer'es with the true shades of dyes produced from the benzene and renders toxic those pharmaceutical products originating from the benzene as well as poisons catalysts used in catalytic processes, the complete removal of the varying amounts of thiophene contained in the benzene assumes importance.

Many procedures for removing thiophene from benzene have been proposed. Among such prosulphuric acid).

' accordance with 2 cedures may be mentioned the reaction with aluminum chloride, or by the use of sulphuric acid of 66 B. gravity,.or even more concentrated sulphuric acid, or by the use of oleum (fuming For the present purposes, all prior methods fail because the thiophene either is only partially removed or there is excessive sulphonation of the benzene, or the cost of equipment and maintenance is excessive.

' The present process provides a procedure for removing thiophene from benzene either completely, phene is so small or to an extent wherein any residual thioin amounts as to be undetectable by the most sensitive reactions therefor.

In accordance with the present invention, the

motor benzene, the pure benzene or the primary light oil referred to above herein is treated for the complete removal of thiophene. The motor grade benzene is a grade that is suitable as motor fuel and contains toluol and xylol. The pure benzene is what is referred to as industrially pure, and both grades contain thiophene, the amounts of which depend upon the quality of the coal from which the benzene has been obtained. Thus, some of these benzenesand/or light oils are found to contain only from about 0.001 percent to 0.002 per cent thiophene, while others contain upwards of 0.03 per cent of thiophene, or

. more. Even such small amounts of thiophene as the 0.001 per cent mentioned above are objectionable and render the benzene unacceptable for the purposes indicated above herein.

The present invention is based upo'ii the discovery that this thiophene may be removed entirely, or at least to such low limits as to be'undetectable by the most sensitive tests now known; that is, the thiophene is removed by the present process either completely, or at least to below 0.000035 per cent, which is the limit of the sensitivity of the standard isatin reaction for thiophene. In carrying out tor" benzene, the pure'? benzene and theprimarylight oil referred to above are treated in the following specific examples which are illustrative of the process.

The process of the present invention involves, importantly, a conjoint action of sulphuric acid and starch, it being found that the presenceof the starch effects the complete removal of the thiophene, which complete removal cannot be accomplished by the sulphuric acid alone, as willbecome apparent from the following illustrative examples of the process. While it will be seen from the examples of the process that the sulphuric acid alone effects'some removal of thiophene, such removal isv incomplete and does not remove the thiophene below objectionable amounts,

my form of starch may be employed, such as corn, wheat or potato starch, but corn starch is preferred for economicreasons.

Example I I Five thousand five hundred gallons of motor benzene were charged intoa suitable agitator and 140 pounds of starch were added. After the starch became thoroughly distributed through the benzene, I20 pounds of 66 added, and the entire resulting mixture was agitated at atmospheric temperatures for approximately 1% hours. The sludge then was drained off, the batch neutralized with 20 per cent caustic soda solution-and the resulting neutral oil was charged intoa fractionating still. Pure thiophene-free benzene was recovered by fractional the present invention the modistillationu The comparable analysis of the charge and the product was as follows:

Freezin int Thio 115112.-.- Tot sulphur..-

l Refers to a possible maximum of 0.000035 per cent which is the limit of the sensitivity of the isatin reaction.

Example If Industrially pure benzene with a thiophene content of 0.03% was found to require larger amounts of sulphuric acid than were employed inExample I.

After preliminary tests had indicated that concentration of 8 per cent by volume of 66 B. sulphuric acid would be required for the removal of a thiophene content of 0.03per cent, a sample of industrially pure benzene with' a freezing point of 5.1? C. and thiophene co'ntentof 0.03 er cent, was divided into three portions and treated as follows:

1. The first portion was reserved for untreated fractional distillation only.

2. The second portion was treated wit 8 per cent, by volume, of 66 B. sulphu acid. agitated thoroughly for thirty minutes, neutralized with caustic soda, steam distilled. and then fractionated to recover pure benzene. 4

3. The third portion was mixed with starch inthe ratio of 140 pounds per 5,500 gallons, treated with 8 per cent, by volume, of 66 B. HaSO4.

agitated thoroughly for 30 minutes, neutralized with 20 per cent caustic soda solution, steam distilled, and fractionated to recover pure benzene. The comparative results are shown in the following table.

These portions are identified in the table as Por- Volume Portionl Portigilil Portlon3 I Thio- Thio- 'lhlo ofdistrlfreezing frecz freezing late point phene point, phene point phene c.c. c. .Ptrmu 0. Percent w? Percent it 5'? E8 50 512' 5122 11.22 I 50 5.24 5.24 5.25 g 1 2'33 2'3? it 60 5125 5123 6224 50 5.25 5. 21 5.23

60 5111 5104 5113 50 5.06 e90 e95 50 4.20 0.03 4.40 0.005 4.30 Nil Residue.

The foregoing examples show the highly advantageous results produced by the action of starchon the thiophene content, whichis re- B. sulphuric acid were moved completely, or at least below the limit of sensitiveness of isatin (0.000035%).

The isatin test for thiophene is carried out by adding 1 c. c. of'the sample which may contain thiophene to 25 c. c. of a 0.05 per cent (weight per volume) solution of isatinin pure H2804, contained in a c. c. cylinder. To the mixture then are added 25 c. c. of pure H2504 containing one drop of concentrated HNOa. Upon mixing, the appearance of a blue or green color within two hours indicates the presence of thiophene. The

unsaturated compounds from the oil, and, therefore, none of these can contaminate the recovered benzene.

In the process only inexpensive commercial reagents are employed, reactant losses are negligible, and there is no appreciable sulphonation of the benzene.

The impurities, including the thiophene, which are removed by the starch-sulphuric acid treatment, together with the starch,- collect as a sludge which is separable readily from the remainder of the treated material.

In addition to starch, other materials may be employed in a similar manner, for example sucrose and cellulose.

We claim:

1. The process of recovering thiophene-free benzene from light oil produced in coal distillation, which comprises washing the light oil with sulphuric acid to remove unsaturated compounds present in the oil, neutralizing the resulting acidifled oil, separating the neutralized oil, distilling the said oil to recover therefrom various grades of benzene which contain thiophene among their impurities, treating the said benzene with starch or starch-yielding substances and sulphuric acid in amounts sufllcient to remove the thiophene contained in the benzene, agitating the benzene with the starch and sulphuric acid until the thiophene contained in the benzene isreduced to from below 0.000035 per cent to complete removal, and

recovering thiophene-free benzene therefrom.

2. In the process of recovering thiophene-free benzene from thiophene-containing benzene, the

improvement which consists in completely re-; moving the thiophene by agitating the thiophenethan"66 B. gravity, separating rthe treated benzene from the sludge resulting from the agitation, neutralizing the benzene, and recovering thiophene-free benzene therefrom.

4. The process of recovering thiophene-free i 3 benzene from thiophene-containing benzene, which comprises agitating the thiophene-containing benzene with starch or starch-yielding substances in the presence of sulphuric acid, the

starch and acid being proportioned in quantity to the amount of thiophene contained in the benzene being treated so as to effect complete removal of'the said thiophene, continuing to agis 'tate the benzene with the starch and acid until reaction with the thiophene is complete, the acid being below a strength suflicient to produce appreciable sulphonation of the benzene, neutralizing the thus treated benzene, and recovering thiophene-free benzene therefrom.

5. The process of recovering. thiophene-free benzene from thiophene-containing benzene, which comprises agitating the thiophene-containing benzene with starch or starch-yielding substances in the presence of 66 B. gravity sulphuric acid, the starch and acid being in quanti-. ties suflicient to remove the thiophene completely from the benzene, continuing the agitation until complete removal of the thiophene is effected as indicated by a negative reaction with isatin, neutralizing the thus treated benzene with caustic soda, and recovering thiophene-free benzene from the thus neutralized benzene.

6. The process of recovering thiophene-free acid being inquantities suflicient to remove the thiophene from the light oil, neutralizing the thus treated light oil with caustic soda and recovc ring the thiophene-free benzene by fractional distillation of the thus neutralized light oil.

7. The process of recovering thiophene-free benzene from thiophene-containing benzene which comprises agitating the thiophene-containing benzene with sulphuric acid of approximately 66 B. gravity and in the presence of a substance selected from the group consisting of starch, sucrose, and cellulose, the acid and substance being in quantities suillcient to remove the thiophene completely from the benzene, continuing the agitation until complete-removal of the thiophene is effected as indicated by a negative reaction with isatin, neutralizing the thus treated benzene with caustic soda and recovering thiophene-free. benzene from the thus neutralized benzene.

8. The processes claimed in the said substance is cellulose.

9.- Eihe process as claimed insclaim the said substance is sucrose.

HEBER VON GEORGE CHARLES PONCHAUD.

claim L wherein 7 .;wherein... 

